The invention relates to a device for the automatic stepped cable length adjustment of a Bowden cable system characterised by a simple construction, reliable functioning and the possibility of being made optionally from plastics or metal.
Cable length adjustment devices are generally used where cables are used as force-transferring members and the cable lengthening which occurs due to such force transference must be compensated in order to maintain proper functioning of the system.
Devices of this kind are particularly widespread for so-called Bowden window regulators for lifting and lowering the side window panes of motor vehicles. Common to many cable length compensating devices is the use of two parts displaceable relative to each other which are held under tension by a spring and then carry out an adjusting movement when cable slack occurs. This adjusting movement corresponds in effect to a lengthening of the Bowden tube.
Furthermore it is known from DE 38 05 046 C2 to lock by means of detent elements the relative position of the two relatively displaceable parts. This position is reached following the adjusting movement. A number of narrow detent elements lying one above the other and which can fall one after the other behind the free end of the displaceable part ensures a finely stepped cable length compensation. This device is however not in a position to differentiate between a so-called genuine cable slack and an apparent cable slack which occurs in the event of high strain on a cable loop of a cable window regulator in the unloaded area of the cable loop, for example, when the window pane reaches its full end stop position at the end of a lifting or lowering operation. Thus considerable tensions can appear in the system which through increased friction lead to deterioration in the degree of efficiency of the adjustment device and to accelerated wear.
From EP 0 658 696 A1 a cable length adjustment device is known having a tubular part on the housing side and a part on the Bowden tube side mounted displaceably therein. The Bowden tube is supported on one side on the part on the Bowden tube side and a compression spring is supported on the other which directs a force on the part on the Bowden tube side in the direction of the Bowden tube. Several slits are formed circumferentiaiiy and spread out in the wall of the tubular part on the housing side through which detent teeth of an elastic open ring can engage and enter into engagement with the counter teeth of the part on the Bowden tube side.
The expansion of the slits in the displacement direction is greater than the height of the detent teeth so that during a displacement movement of the part on the Bowden tube side, first the detent teeth of the elastic ring are dragged along by the detent teeth until it reaches the boundary face of the slits acting as stops. Only a displacement movement beyond this results in relative movement between the elastic ring and the part on the Bowden tube side and in a permanent, i.e., locked setting movement (cable length compensating movement). In other words, the displacement movement must be at least the sum of the axial play of the elastic ring in the slits of the part on the housing side and of the division of the permanent saw-tooth like teeth of the part on the Bowden tube side to result in a permanent cable length compensating movement. In each case, the predetermined axial play is available for relaxing the tension in the system in that the supporting forces of the Bowden tube cause a restricted, non-permanent, resetting movement of the displaceable part on the Bowden tube side until the detent teeth of the elastic ring have reached the other stop of the slits.
However the device described has the drawback that the spring elastic ring supporting the detent teeth can only be made of plastic owing to the large expansion required for assembly. Thus the forces which can be transferred by same are duly restricted.
A device which is identical in operation and very similar in construction is described in WO 96/25604. It also consists of a part on the housing side and a sleeve-like part on the Bowden side displaceable therein and having external teeth in which the teeth of a locking element can engage. The locking element of this device is also mounted displaceably between two stops so that the system is provided with an axial longitudinal play which prevents excess tension of the adjustment device.
It is however disadvantageous that the inner arrangement of the detent element leads to the formation of comparatively small detent teeth. In conjunction with the locking element which has to be made from plastic owing to the demand for elastic deformability, this device can also only be loaded to a restricted amount.